1. Field of the Invention
The present invention relates to an apparatus and method for driving a liquid crystal display (LCD) device, in which an inversion method of an LCD panel is changed depending on a specific pattern of image data so as to improve picture quality of images displayed on the LCD panel.
2. Discussion of the Related Art
Generally, an LCD displays images by controlling light transmittance of a liquid crystal having dielectric anisotropy using an electric field. To this end, the LCD device includes an LCD panel having pixel regions arranged in a matrix arrangement and a drive circuit for driving the LCD panel.
The LCD panel includes a plurality of gate lines, a plurality of data lines, and pixel regions, wherein the gate lines are arranged to cross the data lines and the pixel regions are disposed in regions defined by vertically crossing the gate lines and the data lines. The LCD panel further includes pixel electrodes and common electrodes formed to apply an electric field to each of the pixel regions. Each of the pixel electrodes is connected to a thin film transistor (TFT) which serves as a switching device. The TFT is turned on by scan pulses of the gate lines so that data signals of the data lines are charged in the pixel electrodes.
The driving circuit includes a gate driver for driving the gate lines, a data driver for driving the data lines, a timing controller supplying control signals for controlling the gate driver and the data driver, and a common voltage generator supplying a common voltage to the LCD panel.
In the aforementioned LCD device, various inversion driving methods are used to drive the liquid crystal cells on the LCD panel, such as frame inversion, line-column inversion, and dot inversion.
In the frame inversion driving method, the polarity of the data signals supplied to the liquid crystal cells on the LCD display panel is inverted whenever a frame is changed. In the line-column inversion driving method, the polarity of the data signals supplied to the liquid crystal cells is inverted according to the line (column) on the LCD panel. In the dot inversion driving method, a data signal is supplied to each liquid crystal cell of the LCD panel, wherein the data signal has a polarity contrary to the data signal supplied to adjacent liquid crystal cells along vertical and horizontal directions. In addition, in the dot inversion driving method, the polarity of the data signals supplied to all the liquid crystal cells on the LCD panel is inverted for each frame.
Among the various inversion driving methods, the dot inversion driving method provides excellent picture quality, as compared to the frame and line-column inversion methods. According to the inversion driving method, the data driver responds to a polarity control signal supplied from the timing controller to the data driver.
In the dot inversion driving method, as shown in FIG. 1, a pixel voltage of positive polarity or negative polarity is repeatedly applied to the liquid crystal cell in a direction of the gate lines of the LCD panel, and data levels of black (B), white (W), B, W, . . . , or W, B, W, B, . . . are repeatedly displayed. In this case, a defect in picture quality, such as greenish and crosstalk, occurs due to distortion of the common voltage in a dot pattern such as a windows shutdown pattern.
In more detail, in the dot inversion driving method, as shown in FIG. 2, a data voltage of positive polarity (+) and a data voltage of negative polarity (−) are repeatedly supplied for the unit of one horizontal line. In this case, if the data voltage of positive polarity (+) is supplied more than the data voltage of negative polarity (−) during display of white or black, the common voltage Vcom is changed to positive polarity (+).
As the data voltage has the aforementioned polarity pattern, the data voltage of positive polarity (+) and the data voltage of negative polarity (−) supplied to one horizontal line (one gate line) are different from each other in their output range. For this reason, the common voltage Vcom becomes unbalanced. As a result, the common voltage is swung (Vcom-swing) toward the data voltage of positive polarity (+) or the data voltage of negative polarity (−) for the unit of one horizontal line. Also, as shown in FIG. 2, the liquid crystal cell of green (G) becomes relatively brighter than the liquid crystal cell of red (R) and the liquid crystal cell of blue (B), whereby a greenish color occurs on the LCD panel.
Such a greenish color on the LCD panel may occur in two-dot inversion driving method in accordance with the polarity pattern of the data voltage.